The commander's comments come amid concerns from Congress that the Pentagon is considering reducing the number of U.S. troops on the continent.
Trump's plan for a huge increase in defense spending next fiscal year would mean billions more for equipment and training.
Vice Adm. Shoshana Chatfield represented the U.S. in NATO's Military Commission, the alliance's leading military board.
A Chinese military ship monitored the maneuvers off the Scarborough Shoal from a distance.
